S

simatos

Well Known Member
Running engine sensor hook ups now. A little confused on how to hook up the tach sensor wires to the P Mag. The three wire bundle in question shows the following on the schematic:

12 volt hi
tach sensor
12 volt lo

And the P Mag has 6 possible spots for hook up. Anyone have an idea where the 3 wires go on the P Mag?

Thanks G
 
Hi Gary,

For the Pmag or other E.I., you don't use the tach sensor wiring....it's for a mag sensor which you are not using. Instead, you use a single shielded wire to the RPM input. See page 24-2 of the install manual for a pictorial representation (and no, I'm not that smart, I just keep a copy of the manual on my iPad)! :)

Cheers,
Stein
 
Make sure to read your P-mag manual! (It is available on their website.)

This is your ignition you are asking about, you want to make sure it is wired correctly! "Wired correctly," means as described in the manual.

I can't tell you how many people I have helped with their P-mags only to find out they did not read and/or understand the manual.
 
The pmag manual is available here.

The way I'm understanding this is that you can take the shielded three wire lead you have now and connect the "tach sensor" wire to position 6 on the pmag control connector, and optionally connect the ground wire to aircraft ground for a cleaner signal. In effect the pmag takes care of the 12v and ground going to the sensor on its own.
 
flyeyes said:
The pmag manual is available here.

...
and optionally connect the ground wire to aircraft ground for a cleaner signal. In effect the pmag takes care of the 12v and ground going to the sensor on its own.
Click to expand...

It is very important to read the manual so you understand which pin is position six AND that you must stiill ground each P-mag to an independent case bolt. While you can add an additional ground between the P-mags and your airframe, the engine case grounds are extremely important.
 
N941WR said:
It is very important to read the manual so you understand which pin is position six AND that you must stiill ground each P-mag to an independent case bolt. While you can add an additional ground between the P-mags and your airframe, the engine case grounds are extremely important.
Click to expand...

Absolutely, and just to be clear, I'm suggesting taking the ground wire from the shielded three wire lead to aircraft ground.

The pmag itself is grounded to any convenient stud on the engine case using an 18 gauge wire from pin 1 on the connector, not to airframe ground.

You certainly don't want to ground the pmag through the sensor ground pin on the GSU73
 
So here is the next bone headed question. The connection for "tach" is the number 6 station on the P mag. I think we are in agreement. From The Garmin Install Manual for P mag you have a single wire going back to GEA 24 at what looks like pin 17(RPM) if i read this right. The existing 3 wire bundle come from pin 7, 8 and 9. The number 17 pin is actually associated with the oil pressure transducer. So the problem is which connection from the GEA 24 do I use. I hope i am reading the schematics wrong, Any thoughts??? Mabe it would be easier to pull the tach signal off the regular mag cause i have one of each. Thanks G
 
simatos said:
So here is the next bone headed question. The connection for "tach" is the number 6 station on the P mag. I think we are in agreement. From The Garmin Install Manual for P mag you have a single wire going back to GEA 24 at what looks like pin 17(RPM) if i read this right. The existing 3 wire bundle come from pin 7, 8 and 9. The number 17 pin is actually associated with the oil pressure transducer. So the problem is which connection from the GEA 24 do I use. I hope i am reading the schematics wrong, Any thoughts??? Mabe it would be easier to pull the tach signal off the regular mag cause i have one of each. Thanks G
Click to expand...

I don't have a GEA 24, and I'm not an expert, but it looks to me like the GEA 24 is looking for a frequency input (12V square wave) on pin 8 for RPM1 and pin 6 for RPM2. The Pmag will send this signal at 2 pulses/rev.

The other two wires, +12V and ground, are used for sensors like a westach RPM transducer that requires voltage and ground to output a frequency.

I think if you take the wire from pin 8 of the GEA 24 and connect it to position 6 on the Pmag, you'll be fine. Connecting the wire from pin 7 on the GEA 24 to aircraft ground may help if the signal is "noisy."

I would double check this with someone who is a real expert, but I'm thinking you don't have to take the GEA 24 connector apart.
 
Simatos,
I have my left P-Mag connected to GEA24 P243 pin 8 and right connected to pin 6. Pin 17 is oil pressure.
 
Last edited:
Ouch! Thanks James you are correct. I changed my previous comment.
The P-Mag does not use the ground Pin 7 or 5 however.
 
Thanks you guys, New wrinkle: The Aircraft Spruce keyed switch has a jumper you can use to ground your right mag while you start on the left one. The thinking is to not use it (the right one) during start up as it is not retarded and may give rise to a backfire. In the installation for the P mag they ask that this jumper be removed but wouldn't the same risk of backfire exist with a P mag??????
 
Since the P-Mag uses electric and vacuum advance it is retarded at low RPM's ie start-up . Use the P-Mag during start.
 
You must log in or register to reply here.